The number of migrants stopped at Germany's borders has doubled, while voluntarily deportations are also on the rise. The issue is set to be a major political issue ahead of elections next year.

An increasing number of migrants are voluntarily leaving Germany to return to their homelands and police are refusing entry to more people at the border, according to media reports on Wednesday citing official statistics.

So far this year around 55,000 migrants voluntarily left Germany to return to their country of origin, the largest number in 16 years, the daily "Süddeutsche Zeitung" reported. The number is nearly double the estimated 25,000 forced deportations carried out so far this year.

Most of the migrants came from the western Balkans, with around 15,000 people returning to Albania up to November. That was followed by another 5,000 migrants each from Serbia, Kosovo and Iraq. The figures are based on internal documents from the Federal Office for Migration and Refugees (BAMF).

People from the Balkans have little chance of receiving permanent residency rights in Germany. By voluntarily repatriating, they avoid forced deportation and a permanent ban on reentering Germany.

They may also be eligible for monetary support. A migrant family of five from Afghanistan, for example, may receive 4,200 euros ($4,400) in addition to a flight, travel money and other funds that can add up to between 1,000 and 3,000 euros per person. Germany has controversially labeled Afghanistan a "safe country of origin" and recently upped the number of repatriations to the war-torn country.

Parallel to an upswing in voluntary repatriation, German police have denied entry at land borders, ports and airports to 19,720 people between January and November 2016. That compares to 8,913 entry denials in all of 2015. A large portion of those stopped at the border came from Afghanistan, Syria, Iraq and Nigeria, according to the "Neue Osnabrücker Zeitung" newspaper.

The German government reimposed border controls at the height of the migration crisis in September 2015. But the number of migrants stopped at the border is deceptive as the border controls were implemented only with Austria, meaning migrants may have entered using alternative routes. Nearly 75 percent of border denials were at the Austrian-German border.

The influx of more than a million asylum seekers from war-torn countries and economic migrants over the past two years has had major political and social effects in Germany. The political backlash, which has only grown in the wake of a series of terror attacks in Germany, has provided political ammunition to the right-wing, populist Alternative for Germany (AfD) and led to divisions between Chancellor Angela Merkel's Christian Democrats (CDU) and its Bavarian sister party, the Christian Social Union (CSU).

The political infighting between the CDU and CSU is playing out ahead of federal elections next year, in which Merkel is running for a fourth term. Merkel has stood by her open-door refugee policies, even as she pushes a controversial migrant deal with Turkey and the closure of the main Balkan route used by migrants to reach Europe which has stemmed the flow of new arrivals.

The CSU wants a cap on migrants entering Germany and strengthening of borders, a policy position that has driven a deep wedge between it and Merkel. In the wake of this month's terror attack on a Berlin Christmas market, killing 12 people and wounding nearly 50, the CSU has renewed calls for a shift in Germany's migration policy.

The suspected attacker, 24-year-old Tunisian Anis Amri, used multiple aliases and avoided deportation because he did not have ID documents. The belief that the attack could have been prevented has prompted criticism in Germany over the apparent security lapse that enabled the radicalized asylum seeker to avoid deportation.

"The Amri case raises questions - questions that are not only tied to this crime but also to the time before, since he came to Germany in July 2015," Merkel said in the days following the terrorist attack. "We will now intensively examine to what extent official procedures need to be changed."

Many asylum-seekers and migrants have arrived in Germany without ID documents, either because they don't have them or they purposefully destroyed them knowing it would slow down deportation. Now the CSU is calling for restricting entry to people without ID documents, according to an internal proposal written up by the party ahead of a policy conference, the "Passauer Neue Presse" newspaper reported.

Whoever arrives at the border without a passport or other ID documents should be "held at the border and stay in transit centers until their identity is clarified," the CSU's Bavarian state lawmakers proposed in a policy paper.

"We should not allow people with multiple identities, such as the Berlin attacker, to travel throughout Europe and avoid authorities," the policy paper said.